Optical filter and optical module having optical filter

ABSTRACT

An optical filter includes a first substrate, a first mirror formed on the first substrate, a second substrate coupled to the first substrate, the second substrate including a concave portion, a second mirror formed on the concave portion and facing the first mirror, and an electrode formed on the second substrate and around the second mirror. The first substrate includes a plurality of first hinge portions and a plurality of second hinge portions inside the plurality of first hinge portions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. Pat. Ser. No.12/628,754 filed on Dec. 1, 2009. This application claims priority toJapanese Patent Application No. 2008-313306 filed on Dec. 9, 2008. Theentire disclosures of U.S. Pat. Ser. No. 12/628,754 and Japanese PatentApplication No. 2008-313306 are hereby incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to an optical filter and to an opticalmodule that is provided with the optical filter.

2. Related Art

Conventional air-gap-type electrostatically actuated optical filters areknown as optical filters for selectively emitting a desired wavelengthof light from incident light. In such filters, a pair of substrates arearranged facing each other, a mirror is provided to each of the opposingsurfaces of the substrates, electrodes are provided on the periphery ofthe mirrors, a diaphragm portion is provided on the periphery of onemirror, and the diaphragm portion is displaced by electrostatic forcebetween the electrodes to vary the gap (air gap) between the mirrors,whereby the desired wavelength of light is extracted (see JapaneseLaid-Open Patent Publication No. 2003-57438 and Japanese Laid-OpenPatent Publication No. 2008-116669, for example).

In such an optical filter, the gap between the pair of mirrors must becontrolled in an extremely narrow range of less than one micron toseveral microns during manufacturing, and it is important that the gapbetween the mirrors be precisely maintained and controlled to thedesired size.

In such an optical filter, the wavelength of light that corresponds tothe gap between the mirrors can be selectively extracted by varying thegap between the mirrors.

SUMMARY

In the conventional air-gap-type electrostatically actuated opticalfilter, since the spectral characteristics of the extracted lightdecline when the parallelism between the mirrors or the degree offlatness of the mirrors is reduced, keeping the pair of mirrors paralleland flat is most important for maintaining the characteristics of theoptical filter.

However, when the gap between the mirrors is made variable by air gapelectrostatic actuation in order to selectively extract the desiredwavelength of light from the optical filter, bending of the diaphragmportion is propagated to the mirror on the movable side, and the mirrorcurves and the flatness thereof is reduced. Consequently, the maximumtransmittance of the extracted light is reduced, and a so-called broadwaveform having an increased half bandwidth is exhibited. As a result,severe adverse effects occur in the spectral characteristics of theextracted light.

The present invention was developed in order to overcome the problemsdescribed above, it being an object thereof to provide an optical filterand optical module provided with the same whereby bending thataccompanies variability of the gap between the mirrors can be preventedfrom propagating to the mirror on the movable side, and as a result,light having high maximum transmittance, a narrow half bandwidth, andexcellent spectral characteristics can be extracted, and the spectralcharacteristics of the extracted light can be satisfactorily maintainedwithout adversely affecting the spectral characteristics, even when thegap between the mirrors is made variable in order to selectively extractthe desired wavelength of light.

In order to overcome the problems described above, the present inventionemploys the optical filter and optical module provided with the opticalfilter as described below.

An optical filter according to a first aspect of the invention includesa first substrate, a first mirror formed on the first substrate, asecond substrate coupled to the first substrate and including a concaveportion, a second mirror formed on the concave portion and facing thefirst mirror, and an electrode formed on the second substrate and aroundthe second mirror. The first substrate includes a plurality of firsthinge portions and a plurality of second hinge portions inside theplurality of first hinge portions.

In the optical filter of this aspect of the present invention, at leastone second hinge portion is formed on one or both of the innerperipheral side and outer peripheral side of the first hinge portion.Bending that occurs in the first hinge portion is thereby mitigated bythe second hinge portion, and the amount of bending propagated to themirror on the movable side is reduced even when the gap between themirrors is made variable in order to selectively extract the desiredwavelength of light from the optical filter. Curving of the mirror onthe movable side due to this bending is thereby minimized, reduction ofthe flatness of the mirror is minimized, and the light extracted fromthe mirrors has high maximum transmittance and a narrow half bandwidth.Light having excellent spectral characteristics can thereby beextracted, and the spectral characteristics of the extracted light canbe satisfactorily maintained without adversely affecting the spectralcharacteristics.

It is thereby possible to provide an optical filter whereby light havingexcellent spectral characteristics can be extracted, and the spectralcharacteristics of the extracted light can be satisfactorily maintainedwithout adversely affecting the spectral characteristics.

In the optical filter as described above, at least one of the pluralityof the first hinge portions may have a first beam width, at least one ofthe plurality of the second hinge portions may have a second beam width,and the first beam width may be equal to or larger than the second beamwidth.

In this optical filter, the beam width of the second hinge portion isequal to or less than the beam width of the first hinge portion. Bendingin the first hinge portion is thereby more efficiently mitigated by thesecond hinge portion, and the amount of bending propagated to the mirroron the movable side is significantly reduced. The amount of curving ofthe mirror on the movable side that occurs due to the bending is therebymade extremely small, reduction of the flatness of the mirror is madeextremely small, the maximum transmittance of the light extracted fromthe mirrors is extremely high, and the half bandwidth thereof isextremely narrow. Light having excellent spectral characteristics canthereby be extracted, and the spectral characteristics of the extractedlight can be satisfactorily maintained without adversely affecting thespectral characteristics.

In the optical filter as described above, the at least one of the firstand second substrates is preferably made of semiconductor material.

In this optical filter, making one of the first substrate and the secondsubstrate a semiconductor material enables use of electromagnetic waves,e.g., near-infrared rays that are capable of passing through thesemiconductor material as the incident light. The range of wavelengthsof the incident light is thereby increased.

An optical module according to another aspect of the invention includesthe optical filter according to the aspect as described above.

Providing the optical module with the optical filter according to theaspect of the present invention makes it possible to provide an opticalmodule that is capable of extracting light having a high maximumtransmittance, a narrow half bandwidth, and excellent spectralcharacteristics, and of maintaining satisfactory spectralcharacteristics of the extracted light without adversely affecting thespectral characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a plan view showing the optical filter according to the firstembodiment of the present invention;

FIG. 2 is a sectional view showing the optical filter according to thefirst embodiment of the present invention;

FIG. 3 is a view showing the relationship between the wavelength andtransmittance when a voltage is not applied in the optical filteraccording to the first embodiment of the present invention;

FIG. 4 is a schematic view showing the state of bending when a voltageis applied in the optical filter according to the first embodiment ofthe present invention;

FIG. 5 is a view showing the relationship between the wavelength andtransmittance when a voltage is applied in the optical filter accordingto the first embodiment of the present invention;

FIG. 6 is a sectional view showing the optical filter according to thesecond embodiment of the present invention;

FIG. 7 is an enlarged sectional view showing the relevant portion of theoptical filter according to the second embodiment of the presentinvention;

FIG. 8 is a plan view showing the optical filter according to the thirdembodiment of the present invention;

FIG. 9 is a sectional view showing the optical filter according to thethird embodiment of the present invention;

FIG. 10 is a view showing the results of a simulation of thecurvature-reducing effects of the optical filter of the presentinvention; and

FIG. 11 is a view showing an embodiment of the optical filter devicemodule of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Preferred embodiments of the optical filter and optical module providedwith the optical filter of the present invention will next be described.

An air-gap-type electrostatically actuated optical filter will bedescribed as the optical filter.

In the following description, an XYZ orthogonal coordinate system isset, and the positional relationships of members will be described withreference to this XYZ orthogonal coordinate system as needed. In thissystem, a predetermined direction in the horizontal plane is designatedas the X-axis direction, the direction orthogonal to the X-axisdirection in the horizontal plane is designated as the Y-axis direction,and the direction orthogonal to the X-axis direction and Y-axisdirection (i.e., the vertical direction) is designated as the Z-axisdirection.

First Embodiment

FIG. 1 is a plan view showing the optical filter of the presentembodiment, and FIG. 2 is a sectional view showing the optical filter ofthe present embodiment. In the drawings, the reference numeral 1 refersto an optical filter including an air-gap-type electrostaticallyactuated etalon element, and this optical filter 1 includes a firstsubstrate 2; a second substrate 3 joined (or bonded) to the firstsubstrate 2 so as to face the first substrate 2; a circular mirror 4A (amirror member) provided at the center of an opposing surface 2 a of thefirst substrate 2; a circular mirror 4B (a mirror member) provided tothe bottom of a first cavity 5 formed in the center of the secondsubstrate 3, the circular mirror 4B being provided opposite the mirror4A across a first gap G1; a ring-shaped electrode 6A provided on theperiphery of the mirror 4A of the first substrate 2; a ring-shapedelectrode 6B provided in a shallow ring-shaped second cavity 7 formed onthe periphery of the first cavity 5 of the second substrate 3, andopposite the electrode 6A across a second gap G2; a ring-shaped firstdiaphragm portion 8 having a small wall thickness formed by etching(selective removal) in the first substrate 2 in a position thatsubstantially corresponds to the outer peripheral part of the electrode6A; and a ring-shaped second diaphragm portion 9 having a thicknessequal to or less than that of the diaphragm portion 8, and formed byetching (selective removal) in the first substrate 2 outside the mirror4A and on the inner peripheral side of the diaphragm portion 8. As shownin FIGS. 1 and 2, in this embodiment, the first substrate 2 includes afirst portion located on the mirror 4A, a second portion located aroundthe first portion, a third portion located around the second portion,and a fourth portion located around the third portion. The secondportion of the first substrate 2 corresponds to the second diaphragmportion 9, and the fourth portion of the first substrate corresponds tothe first diaphragm portion 8.

The diaphragm portion 8 and the electrodes 6A, 6B provided opposite eachother across the second gap G2 constitute an electrostatic actuator.

The first substrate 2 and second substrate 3 are both rectangles(squares) of optically transparent material having insulationproperties, and are preferably composed particularly of glass or anothertransparent material.

Specific examples of glass that can be suitably used include soda glass,crystallized glass, quartz glass, lead glass, potassium glass,borosilicate glass, sodium borosilicate glass, non-alkali glass, and thelike.

Making both the first substrate 2 and the second substrate 3 anoptically transparent material enables electromagnetic waves or visiblelight rays having the desired wavelength spectrum to be used as theincident light.

Forming both the first substrate 2 and the second substrate 3 out of asemiconductor material, e.g., silicon, enables near-infrared rays to beused as the incident light.

The mirrors 4A, 4B are arranged facing each other across a first gap G1,and therefore include dielectric multilayer films in which a pluralityof high-refractive-index layers and low-refractive-index layers islayered in alternating fashion. The mirrors 4A, 4B are not limited todielectric multilayer films, and a carbon-containing silver alloy filmor the like, for example, may also be used.

The mirror 4A of the mirrors 4A, 4B is provided to the first substrate2, which is capable of changing shape, and the mirror 4A is thereforereferred to as the movable mirror. The other mirror 4B is provided tothe second substrate 3, which does not change shape, and the mirror 4Bis therefore referred to as the fixed mirror.

When the optical filter 1 is used in the visible light region or theinfrared region, titanium oxide (Ti₂O), tantalum oxide (Ta₂O₅), niobiumoxide (Nb₂O₅), or the like, for example, is used as the material forforming the high-refractive-index layers in the dielectric multilayerfilm. When the optical filter 1 is used in the ultraviolet region,aluminum oxide (Al₂O₃), hafnium oxide (HfO₂), zirconium oxide (ZrO₂),thorium oxide (ThO₂), or the like, for example, is used as the materialfor forming the high-refractive-index layers.

Magnesium fluoride (MgF₂), silicon dioxide (SiO₂), or the like, forexample, is used as the material for forming the low-refractive-indexlayers in the dielectric multilayer film.

The thickness and number of layers of high-refractive-index layers andlow-refractive-index layers are appropriately set based on the requiredoptical characteristics. In general, when a reflective film (mirror) isformed by a dielectric multilayer film, the number of layers needed toobtain the optical characteristics is 12 or more.

The electrodes 6A, 6B are arranged facing each other across the secondgap G2, an electrostatic force is generated between the electrodes 6A,6B according to an inputted drive voltage, and the electrodes 6A, 6Bconstitute a portion of an electrostatic actuator for moving the mirrors4A, 4B relative to each other in a state in which the mirrors 4A, 4B arefacing each other.

The electrodes 6A, 6B are thus configured so that the diaphragm portions8, 9 are displaced in the vertical direction of FIG. 2, the first gap G1between the mirrors 4A, 4B is varied, and light having a wavelength thatcorresponds to the first gap G1 is emitted.

In the present embodiment, since the opposing surface 2 a of the firstsubstrate 2, and the second cavity 7 formed in the second substrate 3are parallel to each other, the electrodes 6A, 6B are also parallel toeach other.

The material for forming the electrodes 6A, 6B is not particularlylimited insofar as the material is conductive, and examples of materialsthat can be used include Cr, Al, Al alloy, Ni, Zn, Ti, Au, and othermetals; resins in which carbon, titanium, or the like is dispersed;polycrystalline silicon (polysilicon), amorphous silicon, and othersilicon; silicon nitride, ITO, and other transparent conductivematerials; and other materials.

As shown in FIG. 1, interconnections 11A, 11B are connected to theelectrodes 6A, 6B, and the electrodes 6A, 6B are connected to a powersupply (not shown) via the interconnections 11A, 11B.

The interconnections 11A, 11B are formed in an interconnection groove12A formed in the first substrate 2, or an interconnection groove 12Bformed in the second substrate 3. Consequently, there is no interferenceat the junction of the first substrate 2 and second substrate 3.

A power supply drives the electrodes 6A, 6B by application of a voltageto the electrodes 6A, 6B as a drive signal, and generates a desiredelectrostatic force between the electrodes 6A, 6B. A control device (notshown) is connected to the power supply, and the power supply iscontrolled by the control device, whereby the difference of potentialbetween the electrodes 6A, 6B can be adjusted.

The diaphragm portion 8 is thinner than the portion of the firstsubstrate 2 in which the diaphragm portion 8 is not formed. The area ofthe first substrate 2 thinner than the remainder thereof is thereforeelastic (flexible) and capable of deformation (displacement), andtherefore the diaphragm portion 8 has wavelength selection capabilitywhereby the desired wavelength of light is emitted by varying the firstgap G1 to change the interval between the mirrors 4A, 4B to the intervalthat corresponds to the desired wavelength of light.

The diaphragm portion 9 is formed between the mirrors 4A, 4B and theelectrodes 6A, 6B that constitute a portion of the electrostaticactuator, and therefore has a smaller thickness than the diaphragmportion 8. Since the diaphragm portion 9 has a thickness equal to orless than that of the diaphragm portion 8, the diaphragm portion 9 ismore flexible than the diaphragm portion 8, and as a result, is able toabsorb bending that occurs in the diaphragm portion 8 and prevent thisbending from propagating to the mirror 4A. Bending that occurs in thediaphragm portion 8 when the first gap G1 is varied can thereby beefficiently mitigated, and the amount of bending that propagates to themirror 4A can be significantly reduced.

The shape or thickness of each of the diaphragm portions 8, 9, theinterval between the diaphragm portions 8, 9, and other characteristicsare arbitrary insofar as light in the desired wavelength range isemitted. Specifically, these characteristics are set with considerationfor the amount of variation, rate of variation, and othercharacteristics of the interval between the mirrors 4A, 4B, and inaccordance with the wavelength range of emitted light needed from theoptical filter 1.

The diaphragm portions 8, 9 are formed by etching (selective removal)from the upper surface of the first substrate 2, but the diaphragmportions 8, 9 are of sufficient thickness insofar as the diaphragmportion 9 can absorb bending that occurs in the diaphragm portion 8 andsuppress propagation of this bending to the mirror 4A, and the diaphragmportions 8, 9 may also be formed by etching (selective removal of) thefirst substrate 2 from both the upper and lower surfaces thereof.

In the optical filter 1 of the present embodiment, when the controldevice and the power supply are not activated, and a voltage is thus notapplied between the electrode 6A and electrode 6B, the mirror 4A and themirror 4B face each other across the first gap G1. Therefore, when lightis incident on the optical filter 1, a wavelength of light thatcorresponds to the first gap G1 is emitted; e.g., light having awavelength of 720 nm is emitted, as shown in FIG. 3.

When the control device and power supply are driven, and a voltage isapplied between the electrode 6A and the electrode 6B, an electrostaticforce corresponding to the size of the voltage (potential difference) isgenerated between the electrode 6A and electrode 6B. The control devicethus controls the power supply, whereby the desired voltage can beapplied between the electrodes 6A, 6B, and the desired electrostaticforce can be generated between the electrode 6A and electrode 6B. Whenthe desired electrostatic force is generated between the electrodes 6A,6B in this manner, the electrodes 6A, 6B are pulled toward each other bythe electrostatic force, the first substrate 2 deforms toward the secondsubstrate 3, and the first gap G1 between the mirror 4A and the mirror4B is made smaller than when a voltage was not applied, as shown in FIG.4.

In this case, the bending that occurs in the diaphragm portion 8 due tothe electrostatic force is absorbed and mitigated by the diaphragmportion 9 on the inside, and the bending that occurs in the diaphragmportion 8 is therefore not propagated as such to the mirror 4A. Theamount of bending propagated to the mirror 4A can therefore be reduced,the curvature of the mirror 4A caused by this bending is minimized, andreduction of the flatness of the mirror 4A is minimized. Bending thatoccurs in the diaphragm portion 8 is thus absorbed by the diaphragmportion 9 and efficiently suppressed, and curvature and reduction of theflatness of the mirror 4A due to this bending are also suppressed. As aresult, there is extremely little curvature of the mirror 4A, and theflatness of the mirror 4A is also satisfactorily maintained.

Since the bending that occurs in the diaphragm portion 8 is absorbed bythe diaphragm portion 9 and efficiently suppressed, and is notpropagated to the mirror 4A, the flatness of the mirror 4A issatisfactorily maintained, and the mirror 4A and mirror 4B face eachother across a stable first gap G1′.

Therefore, when light is incident on the optical filter 1, a wavelengthof light corresponding to the stabilized first gap G1′ and having highmaximum transmittance and a narrow half bandwidth is emitted; e.g.,light having a wavelength of 590 nm is emitted, and the transmittedwavelength is shifted to a shorter wavelength, as shown in FIG. 5.

As described above, in the optical filter 1 of the present embodiment,since a ring-shaped diaphragm portion 9 having a thickness equal to orless than that of the diaphragm portion 8 is formed in the firstsubstrate 2 on the inner peripheral side of the diaphragm portion 8,light having excellent spectral characteristics can be extracted, andthe spectral characteristics of the extracted light can besatisfactorily maintained without adversely affecting the spectralcharacteristics.

Second Embodiment

FIG. 6 is a sectional view showing the optical filter of the presentembodiment, and FIG. 7 is an enlarged sectional view showing therelevant portion of FIG. 6.

In the optical filter 1 of the first embodiment, the ring-shapeddiaphragm portion 9 having a thickness equal to or less than that of thediaphragm portion 8 is formed at a predetermined interval in the firstsubstrate 2 and on the inner peripheral side of the diaphragm portion 8,whereas the optical filter 21 of the present embodiment differs from theoptical filter 1 of the first embodiment in that the diaphragm portions8, 9 are integrated to form a single wide ring-shaped diaphragm portion22. The other constituent elements of the optical filter 21 of thepresent embodiment are the same those of the optical filter 1 of thefirst embodiment.

The shape or thickness of the diaphragm portion 22, and othercharacteristics are arbitrary insofar as light in the desired wavelengthrange is emitted. Specifically, these characteristics are set withconsideration for the amount of variation, rate of variation, and othercharacteristics of the interval between the mirrors 4A, 4B, and inaccordance with the wavelength range of emitted light needed from theoptical filter 21.

The diaphragm portion 22 is formed by etching (selective removal) fromthe upper surface of the first substrate 2, but the diaphragm portion 22is of sufficient thickness insofar as the diaphragm portion 22 canabsorb bending that occurs in the diaphragm portion 22 and suppresspropagation of this bending to the mirror 4A, and the diaphragm portion22 may also be formed by etching (selective removal of) the firstsubstrate 2 from both the upper and lower surfaces thereof.

As described above, in the optical filter 21 of the present embodiment,since the diaphragm portion 22 is formed in the first substrate 2, lighthaving excellent spectral characteristics can be extracted, and thespectral characteristics of the extracted light can be satisfactorilymaintained without adversely affecting the spectral characteristics.

Moreover, by integrating the first diaphragm portion 8 and the seconddiaphragm portion 9 of the first embodiment into the diaphragm portion22 in the second embodiment, the bending occurring in the firstdiaphragm portion 8 that is mitigated by the first diaphragm portion 8and the second diaphragm portion 9 individually is mitigated by theintegrated diaphragm portions 22 at once, and can thereby be moreefficiently mitigated.

Third Embodiment

FIG. 8 is a plan view showing the optical filter of the presentembodiment, and FIG. 9 is a sectional view showing the optical filter ofthe present embodiment.

In the optical filter 1 of the first embodiment, the first substrate 2is formed by glass or another optical transparent material, theelectrodes 6A, 6B are provided to the first substrate 2 and secondsubstrate 3 so as to face each other across the second gap G2, thering-shaped diaphragm portion 8 is formed in a position substantiallycorresponding to the outer peripheral portion of the electrode 6A in thefirst substrate 2, and the ring-shaped diaphragm portion 9 having athickness equal to or less than that of the diaphragm portion 8 isformed on the inner peripheral side of the diaphragm portion 8. However,the optical filter 31 of the present embodiment differs from the opticalfilter 1 of the first embodiment in that a first substrate 32 is formedusing silicon or another semiconductor material, the electrode 6A is notprovided to the first substrate 32, first hinge portions 33 are formedin the first substrate 32 in a plurality of positions (in four locationsin FIG. 8) substantially corresponding to the outer peripheral portionof the electrode 6B, and second hinge portions 34 having a beamthickness equal to or less than that of the first hinge portions 33 areformed in a plurality of positions (in four locations in FIG. 8) outsidethe mirror 4A and on the inner peripheral side of the first hingeportions 33. The other constituent elements of the optical filter 31 ofthe present embodiment are the same as those of the optical filter 1 ofthe first embodiment.

The first hinge portions 33, the electrode 6B, the second hinge portions34, and a second gap G3 between the electrode 6B and the first substrate32 constitute an electrostatic actuator.

The first hinge portions 33 and the second hinge portions 34 are formedso that the longitudinal directions thereof are at 45° angles from eachother.

Specifically, a total of four first hinge portions 33, two parallel tothe X-axis direction and two parallel to the Y-axis direction, areformed at equal intervals on the periphery that substantiallycorresponds to the outer peripheral portion of the electrode 6B.

Four second hinge portions 34 at 45° angles to the X-axis direction andY-axis direction are also formed at equal intervals on the peripherythat substantially corresponds to the outer peripheral portion of themirror 4A, on the inner peripheral side of the first hinge portions 33.

In the optical filter 31 of the present embodiment, when the controldevice is not being driven, the mirror 4A and the mirror 4B face eachother across the second gap G3. Therefore, when light is incident on theoptical filter 1, a wavelength of light that corresponds to the firstgap G1 is emitted; e.g., light having a wavelength of 720 nm is emitted.

An electrostatic force is generated when the control device is driven,the first substrate 32 is deformed toward the second substrate 3 by theelectrostatic force, and the first gap G1 between the mirror 4A and themirror 4B is made smaller than when a voltage is not applied.

In this case, the bending that occurs in the hinge portions 33 due tothe electrostatic force is absorbed and mitigated by the hinge portions34 on the inside, and the bending that occurs in the hinge portions 33is therefore not propagated as such to the mirror 4A. The amount ofbending propagated to the mirror 4A can therefore be reduced, thecurvature of the mirror 4A caused by this bending is minimized, andreduction of the flatness of the mirror 4A is minimized. Bending thatoccurs in the hinge portions 33 is thus absorbed by the hinge portions34 and efficiently suppressed, and curvature and reduction of theflatness of the mirror 4A due to this bending are also suppressed. As aresult, there is extremely little curvature of the mirror 4A, and theflatness of the mirror 4A is also satisfactorily maintained.

Since the bending that occurs in the hinge portions 33 is absorbed bythe hinge portions 34 and efficiently suppressed, and is not propagatedto the mirror 4A, the flatness of the mirror 4A is satisfactorilymaintained, and the mirror 4A and mirror 4B face each other across astable first gap Gr.

Therefore, when light is incident on the optical filter 1, a wavelengthof light corresponding to the stabilized first gap G1′ and having highmaximum transmittance and a narrow half bandwidth is emitted; e.g.,light having a wavelength of 590 nm is emitted, and the transmittedwavelength is shifted to a shorter wavelength.

As described above, in the optical filter 1 of the present embodiment,since first hinge portions 33 are formed in the first substrate 32 in aplurality of positions substantially corresponding to the outerperipheral portion of the electrode 6B, and second hinge portions 34having a beam thickness equal to or less than that of the first hingeportions 33 are formed in a plurality of positions outside the mirror 4Aand on the inner peripheral side of the first hinge portions 33, lighthaving excellent spectral characteristics can be extracted, and thespectral characteristics of the extracted light can be satisfactorilymaintained without adversely affecting the spectral characteristics.

FIG. 10 is a diagram showing the results of a simulation (finite elementanalysis) of the curvature-reducing effects of the optical filter of thepresent invention. In the diagram, “A” indicates the optical filter 1 ofthe first embodiment, “B” indicates the optical filter 21 of the secondembodiment, and “C” indicates the conventional optical filter.

According to FIG. 10, the amount of curvature in the mirror increaseslinearly for all of the structures as the amount of displacement due tovoltage application increases, but the amount of curvature with respectto displacement is smaller in the optical filters 1, 21 of the presentinvention than in the conventional optical filter, and the effects ofthe present invention are confirmed by the simulation results.

For example, 17 μm of curvature occurs in the conventional opticalfilter for 200 μm of displacement, whereas the curvature stays at 10 to11 μm in the optical filters 1, 21 of the present invention, and theamount of curvature can be reduced approximately 40% relative to theconventional optical filter.

An optical filter device module (optical module) provided with theoptical filter 1 (21, 31) will next be described as an application ofthe optical filters 1, 21, 31 of the present embodiments.

FIG. 11 is a view showing an embodiment of the optical filter devicemodule of the present invention, and in FIG. 11, the reference numeral50 refers to an optical filter device module.

The optical filter device module 50 is provided with a filter unit 51including the optical filter 1 (21, 31), and the optical filter devicemodule 50 is configured so that a specific spectrum of light is radiatedto a specimen W, a pre-set wavelength of light is selectively extracted(diffracted) from the light reflected by the specimen W, and theintensity of the extracted light is measured.

Specifically, the optical filter device module 50 is provided with alight source optical system 54 for radiating a predetermined light,e.g., visible light or infrared rays, to the specimen W, the lightsource optical system 54 having a light source 52 and a lens 53; adetector optical system 56 for detecting reflected light from thespecimen W, the detector optical system 56 having a filter unit 51 and adetection element 55; a light source control circuit 57 for controllingthe illumination intensity and other characteristics of the light source52; a filter control circuit 58 for controlling the filter unit 51; anda processor 59 for receiving detection signals detected by the detectionelement 55, the processor 59 being connected to the light source controlcircuit 57 and the filter control circuit 58.

In such an optical filter device module 50, a specific spectrum of lightsuch as visible light or infrared rays is radiated to the specimen W.Light is then reflected according to the surface state of the specimenW, for example, and other factors, and the reflected light enters thefilter unit 51. The filter unit 51 is configured so that a voltage isapplied (or not applied) to the electrodes 6A, 6B so that light having apre-set wavelength is selectively extracted (diffracted). Only aspecific wavelength band is thereby selectively extracted from thereflected light and detected by the detection element 55. Consequently,reflected light can be detected with high sensitivity by using adetection element that selectively detects the light extracted by thefilter unit 51 as the detection element 55, for example.

The optical filter device module 50 thereby enables the surface stateand other characteristics of the specimen W to be detected with highsensitivity.

Since the optical filter 1 (21, 31) described above is used as theoptical filter constituting the filter unit 51, the module is capable ofextracting light having excellent spectral characteristics, and thespectral characteristics of the extracted light can be satisfactorilymaintained without adversely affecting the spectral characteristics.

GENERAL INTERPRETATION OF TERMS

In understanding the scope of the present invention, the term“comprising” and its derivatives, as used herein, are intended to beopen ended terms that specify the presence of the stated features,elements, components, groups, integers, and/or steps, but do not excludethe presence of other unstated features, elements, components, groups,integers and/or steps. The foregoing also applies to words havingsimilar meanings such as the terms, “including”, “having” and theirderivatives. Also, the terms “part,” “section,” “portion,” “member” or“element” when used in the singular can have the dual meaning of asingle part or a plurality of parts. Finally, terms of degree such as“substantially”, “about” and “approximately” as used herein mean areasonable amount of deviation of the modified term such that the endresult is not significantly changed. For example, these terms can beconstrued as including a deviation of at least ±5% of the modified termif this deviation would not negate the meaning of the word it modifies.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. Furthermore, the foregoing descriptions of theembodiments according to the present invention are provided forillustration only, and not for the purpose of limiting the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. An optical filter comprising: a first substrate;a first mirror formed on the first substrate; a second substrate coupledto the first substrate, the second substrate including a concaveportion; a second mirror formed on the concave portion and facing thefirst mirror; and an electrode formed on the second substrate and aroundthe second mirror, the first substrate including a plurality of firsthinge portions and a plurality of second hinge portions disposed insideof the plurality of first hinge portions, the first substrate furtherincluding an intermediate portion arranged inward relative to theplurality of first hinge portions, the intermediate portion connectingeach of the plurality of first hinge portions to one of the plurality ofsecond hinge portions, a first distance between one of the plurality offirst hinge portions and the first mirror being larger than a seconddistance between the one of the plurality of second hinge portions andthe first mirror.
 2. The optical filter according to claim 1, wherein atleast one of the plurality of first hinge portions has a first beamwidth, wherein at least one of the plurality of second hinge portionshas a second beam width, and wherein the first beam width is equal to orlarger than the second beam width.
 3. The optical filter according toclaim 1, wherein the at least one of the first and second substrates ismade of semiconductor material.
 4. An optical module having the opticalfilter according to claim
 1. 5. The optical filter according to claim 1,wherein the intermediate portion has a ring-shape.
 6. The optical filteraccording to claim 1, wherein the second mirror faces the first mirrorin a first direction, and the intermediate portion has a thickness inthe first direction, which is equal to a thickness of a portion of thefirst substrate other than the first and second hinge portions.
 7. Theoptical filter according to claim 2, wherein the first beam width islarger than the second beam width.
 8. The optical filter according toclaim 1, wherein each of the first and second hinge portions has anelongated shape, and an elongated direction of the elongated shape ofeach of the second hinge portions is different from an elongateddirection of the elongated shape of each of the first hinge portions.